Computational repurposing of oncology drugs through off-target drug binding interactions from pharmacological databases

PURPOSE

Systematic repurposing of approved medicines for another indication may accelerate drug development in oncology. We present a strategy combining biomarker testing with drug repurposing to identify new treatments for patients with advanced cancer.

METHODS

Tumours were sequenced with the Illumina TruSight Oncology 500 (TSO-500) platform or the FoundationOne CDx panel. Mutations were screened by two medical oncologists and pathogenic mutations were categorised referencing literature. Variants of unknown significance were classified as potentially pathogenic using plausible mechanisms and computational prediction of pathogenicity. Gain of function (GOF) mutations were evaluated through repurposing databases Probe Miner (PM), Broad Institute Drug Repurposing Hub (Broad Institute DRH) and TOPOGRAPH. GOF mutations were repurposing events if identified in PM, not indexed in TOPOGRAPH and excluding mutations with a known Food and Drug Administration (FDA)-approved biomarker. The computational repurposing approach was validated by evaluating its ability to identify FDA-approved biomarkers. The total repurposable genome was identified by evaluating all possible gene-FDA drug-approved combinations in the PM dataset.

RESULTS

The computational repurposing approach was accurate at identifying FDA therapies with known biomarkers (94%). Using next-generation sequencing molecular reports (n = 94), a meaningful percentage of patients (14%) could have an off-label therapeutic identified. The frequency of theoretical drug repurposing events in The Cancer Genome Atlas pan-cancer dataset was 73% of the samples in the cohort.

CONCLUSION

A computational drug repurposing approach may assist in identifying novel repurposing events in cancer patients with no access to standard therapies. Further validation is needed to confirm a precision oncology approach using drug repurposing.

The Endoscopic Ultrasound Molecular Analysis of Pancreatic Cancer (EUMEPC) study

751

Background: Pancreatic cancer carries a dismal prognosis and limited treatment options. Attempts to implement precision therapies have proved difficult to date, in part due to challenges obtaining high quality genetic material from pancreatic biopsies. Endoscopic ultrasound (EUS) is a common diagnostic procedure, but limited data is available on the clinical utility of these biopsies for comprehensive molecular profiling (CMP) to inform therapeutic choices. Methods: This study aimed to enrol up to 150 patients undergoing EUS biopsies for pancreatic cancer, in order to complete targeted DNA/RNA sequencing on 100. The primary outcome was to characterise the proportion of patients able to undergo CMP on their diagnostic EUS biopsies, with fresh-frozen biopsies preferred but FFPE specimens accepted if there was no alternative. Secondary endpoints included the proportion of patients with clinically relevant molecular findings as determined by Molecular Tumour Board (MTB) discussion, proportion of patients initiating targeted therapies, and quantitative/qualitative analysis on molecular material derived from fresh-frozen versus FFPE EUS biopsies. Results: 109 patients have been enrolled since May 2020, and molecular profiling has been completed for 102 patients. 2 patients (1.8%) were excluded due to having no available biopsies, and 5 biopsies (4.7%) were unable to be sequenced due to inadequate quality metrics. Common oncogenes were detected at roughly expected frequencies, with mutations in KRAS occurring in 91 (89.2%), TP53 in 67 (65.7%), SMAD4 in 11 (10.8%) and CDKN2A in 7 (6.8%). Median tumour mutation burden (TMB) in this cohort was low at 3.1Mut/Mb although 7 patients (6.9%) had a high TMB (defined as >10Mut/Mb), of which 3 (2.9%) had markedly hypermutated tumours (>200Mut/Mb). All processed samples were microsatellite stable. Therapeutically relevant mutations were detected in 21 (20.6%) including RNF43 in 7 patients (6.9%), KRAS G12C and BRCA in 3 patients each (2.9%), in addition to BRAF V600E in 2 (1.9%), and CHEK2 and BARD1 mutations in 1 each (0.9%). High TMB was observed in 7 patients (6.9%). To date, 5 patients (4.9%) have commenced on targeted therapies, with one patient notably experiencing a complete response to targeted therapy which has now been sustained for >12 months. Conclusions: This real-world study confirms the utility of endoscopic biopsies as a valuable and reliable source of genetic material for clinically relevant molecular tumour profiling. Secondary analyses are underway to further characterise treatment and survival implications in this cohort.

A comparative study of techniques for differential expression analysis on RNA-Seq data

Recent advances in next-generation sequencing technology allow high-throughput cDNA sequencing (RNA-Seq) to be widely applied in transcriptomic studies, in particular for detecting differentially expressed genes between groups. Many software packages have been developed for the identification of differentially expressed genes (DEGs) between treatment groups based on RNA-Seq data. However, there is a lack of consensus on how to approach an optimal study design and choice of suitable software for the analysis. In this comparative study we evaluate the performance of three of the most frequently used software tools: Cufflinks-Cuffdiff2, DESeq and edgeR. A number of important parameters of RNA-Seq technology were taken into consideration, including the number of replicates, sequencing depth, and balanced vs. unbalanced sequencing depth within and between groups. We benchmarked results relative to sets of DEGs identified through either quantitative RT-PCR or microarray. We observed that edgeR performs slightly better than DESeq and Cuffdiff2 in terms of the ability to uncover true positives. Overall, DESeq or taking the intersection of DEGs from two or more tools is recommended if the number of false positives is a major concern in the study. In other circumstances, edgeR is slightly preferable for differential expression analysis at the expense of potentially introducing more false positives.

The serum resistome of a globally disseminated multidrug resistant uropathogenic Escherichia coli clone

Escherichia coli ST131 is a globally disseminated, multidrug resistant clone responsible for a high proportion of urinary tract and bloodstream infections. The rapid emergence and successful spread of E. coli ST131 is strongly associated with antibiotic resistance; however, this phenotype alone is unlikely to explain its dominance amongst multidrug resistant uropathogens circulating worldwide in hospitals and the community. Thus, a greater understanding of the molecular mechanisms that underpin the fitness of E. coli ST131 is required. In this study, we employed hyper-saturated transposon mutagenesis in combination with multiplexed transposon directed insertion-site sequencing to define the essential genes required for in vitro growth and the serum resistome (i.e. genes required for resistance to human serum) of E. coli EC958, a representative of the predominant E. coli ST131 clonal lineage. We identified 315 essential genes in E. coli EC958, 231 (73%) of which were also essential in E. coli K-12. The serum resistome comprised 56 genes, the majority of which encode membrane proteins or factors involved in lipopolysaccharide (LPS) biosynthesis. Targeted mutagenesis confirmed a role in serum resistance for 46 (82%) of these genes. The murein lipoprotein Lpp, along with two lipid A-core biosynthesis enzymes WaaP and WaaG, were most strongly associated with serum resistance. While LPS was the main resistance mechanism defined for E. coli EC958 in serum, the enterobacterial common antigen and colanic acid also impacted on this phenotype. Our analysis also identified a novel function for two genes, hyxA and hyxR, as minor regulators of O-antigen chain length. This study offers novel insight into the genetic make-up of E. coli ST131, and provides a framework for future research on E. coli and other Gram-negative pathogens to define their essential gene repertoire and to dissect the molecular mechanisms that enable them to survive in the bloodstream and cause disease.

The emergence and rapid dissemination of new bacterial pathogens presents multiple challenges to healthcare systems, including the need for rapid detection, precise diagnostics, effective transmission control and effective treatment. E. coli ST131 is an example of a recently emerged multidrug resistant pathogen that is capable of causing urinary tract and bloodstream infections with limited available treatment options. In order to increase our molecular understanding of E. coli ST131, we developed a high-throughput transposon mutagenesis system in combination with next generation sequencing to test every gene for its essential role in growth and for its contribution to serum resistance. We identified 315 essential genes, 270 of which were conserved among all currently available complete E. coli genomes. Fifty-six genes that define the serum resistome of E. coli ST131 were identified, including genes encoding membrane proteins, proteins involved in LPS biosynthesis, regulators and several novel proteins with previously unknown function. This study therefore provides an inventory of essential and serum resistance genes that could form a framework for the future development of targeted therapeutics to prevent disease caused by multidrug-resistant E. coli ST131 strains.

Platelets kill intraerythrocytic malarial parasites and mediate survival to infection

Platelets play a critical role in the pathogenesis of malarial infections by encouraging the sequestration of infected red blood cells within the cerebral vasculature. But platelets also have well-established roles in innate protection against microbial infections. We found that purified human platelets killed Plasmodium falciparum parasites cultured in red blood cells. Inhibition of platelet function by aspirin and other platelet inhibitors abrogated the lethal effect human platelets exert on P. falciparum parasites. Likewise, platelet-deficient and aspirin-treated mice were more susceptible to death during erythrocytic infection with Plasmodium chabaudi. Both mouse and human platelets bind malarial-infected red cells and kill the parasite within. These results indicate a protective function for platelets in the early stages of erythrocytic infection distinct from their role in cerebral malaria.

Mice that are congenic for the char2 locus are susceptible to malaria

A major advance has been made towards the positional cloning of char2 (a quantitative trait locus encoding resistance to Plasmodium chabaudi malaria). Mice congenic for the locus have been used to fine map the gene and to prove that char2 plays a significant role in the outcome of malarial infection, independently of other resistance loci.

Exopolysaccharide-producing strains of thermophilic lactic acid bacteria cluster into groups according to their EPS structure

AIMS

To compare galactose-negative strains of Streptococcus thermophilus and Lactobacillus delbrueckii subspecies bulgaricus isolated from fermented milk products and known to produce exopolysaccharides (EPSs).

METHODS AND RESULTS

The structures of the EPSs were determined using nuclear magnetic resonance (NMR) and their genetic relationships determined using restriction endonuclease analysis (REA) and random amplification of polymorphic DNA (RAPD). Similar groupings were apparent by REA and RAPD, and each group produced an EPS with a particular subunit structure.

CONCLUSION

Although none of the strains assimilated galactose, all inserted a high proportion of galactose into their EPS when grown in skimmed milk, and fell into three distinct groups.

SIGNIFICANCE AND IMPACT OF THE STUDY

This information should help in an understanding of genetic exchanges in lactic acid bacteria.

Structural characterisation of the exopolysaccharide produced by Streptococcus thermophilus EU20

Streptococcus thermophilus EU20 when grown on skimmed milk secretes a high-molecular-weight exopolysaccharide that is composed of glucose, galactose and rhamnose in a molar ratio of 2:3:2. Using chemical techniques and 1D and 2D-NMR spectroscopy (1H and 13C) the polysaccharide has been shown to possess a heptasaccharide repeating unit having the following structure: [chemical structure: see text]. Treatment of the polysaccharide with mild acid (0.5 M TFA, 100 degrees C for 1 h) liberates two oligosaccharides; the components correspond to the repeating unit and a hexasaccharide equivalent to the repeating unit minus the terminal alpha-L-Rhap.

Improvements in allelic discrimination of microsatellite markers using denaturing polyacrylamide gel electrophoresis

Poor resolution, retarded progress of DNA through gels, and variable sizing of DNA fragments between and within gels hinder accurate genotyping of some simple sequence length polymorphism (SSLP) markers with the Perkin Elmer Applied Biosystems 377 Sequenator. These problems are similar to renaturation related problems observed in DNA sequencing gels. PCR products especially susceptible to these problems are shown to have higher melting temperatures (T(m)) than others. Gels containing increased concentrations of denaturants allow greater accuracy in allelic discrimination. This is especially beneficial where quantification is necessary.

Temporal expression of an H2-linked locus in host response to mouse malaria

The action of host genes in response to malarial infection is complex. Two mouse loci, Char1, and Char2, have previously been shown to control peak parasitemia and host survival. Recent analysis of host response to mouse malaria has demonstrated that the action of several loci is time dependent. Char1 and Char2 act prior to peak parasitemia. Analysis of additional crosses revealed significant linkage to Chromosome 17 on the day following peak parasitemia. This H2-linked locus acts late in infection and is therefore crucial in clearing parasites from the circulation. The cloning of this gene will lead to a greater understanding of the host-parasite interaction, and the kinetics of host gene expression during an immune response.

Structural and antigenic properties of merozoite surface protein 4 of Plasmodium falciparum

Merozoite surface protein 4 (MSP4) of Plasmodium falciparum is a glycosylphosphatidylinositol-anchored integral membrane protein of 272 residues that possesses a single epidermal growth factor (EGF)-like domain near the carboxyl terminus. We have expressed both full-length MSP4 and a number of fragments in Escherichia coli and have used these recombinant proteins to raise experimental antisera. All recombinant proteins elicited specific antibodies that reacted with parasite-derived MSP4 by immunoblotting. Antibody reactivity was highly dependent on the protein conformation. For example, reduction and alkylation of MSP4 almost completely abolished the reactivity of several antibody preparations, including specificities directed to regions of the protein that do not contain cysteine residues and are far removed from the cysteine-containing EGF-like domain. This indicated the presence of conformation-dependent epitopes in MSP4 and demonstrated that proper folding of the EGF-like domain influenced the antigenicity of the entire molecule. The recombinant proteins were used to map epitopes recognized by individuals living in areas where malaria is endemic, and at least four distinct regions are naturally antigenic during infection. Binding of human antibodies to the EGF-like domain was essentially abrogated after reduction of the recombinant protein, indicating the recognition of conformational epitopes by the human immune responses. This observation led us to examine the importance of conformation dependence in responses to other integral membrane proteins of asexual stages. We analyzed the natural immune responses to a subset of these antigens and demonstrated that there is diminished reactivity to several antigens after reduction. These studies demonstrate the importance of reduction-sensitive structures in the maintenance of the antigenicity of several asexual-stage antigens and in particular the importance of the EGF-like domain in the antigenicity of MSP4.

Heterofermentative metabolism of glucose and ribose and utilisation of citrate by the smooth biotype of Lactobacillus amylovorus NCFB 2745

Lactobacillus amylovorus NCFB 2745 exhibits a rough colony morphology, ferments glucose homofermentatively and cannot utilise ribose. After five transfers in de Man Rogosa and Sharpe media (containing glucose and citrate) Lb. amylovorus 2745 appears smooth on agar plates; smooth cultures reverted to rough by culturing in aerobic conditions. The smooth type shows patterns of fermentation that are typical of a heterofermentative lactobacillus. Thus, the smooth morphotype produces CO2 and ethanol in addition to lactate and is able to ferment ribose. The switch in metabolism to the smooth form is accompanied by an increase in phosphoketolase and a reduction in aldolase enzyme activities. Citrate also has effects on growth rates and end-metabolites.

Close linkage of three merozoite surface protein genes on chromosome 2 of Plasmodium falciparum

We have analysed a 10.5 kb region of chromosome 2 in Plasmodium falciparum that encompasses the coding region of four genes. Three genes are arranged in a head-to-tail orientation and encode the merozoite surface proteins MSP2 and MSP4 as well as a previously unreported sequence that encodes a polypeptide with the characteristics of a merozoite surface protein, now designated MSP5. The fourth gene, asl, is arranged in a tail-to-tail orientation with msp2 and has homology with prokaryotic and eukaryotic genes encoding adenylosuccinate lyase (ASL), an enzyme involved in purine biosynthesis and salvage. The genes, arranged in the order msp4, msp5, msp2 and asl, are separated by intergenic distances of 1021, 1017 and 722 bp, respectively. msp4 and msp5 are clearly related genes, each being composed of 2 exons and encoding proteins of identical length. Both msp4 and msp5 encode proteins that contain hydrophobic signal sequences, apparent glycosylphosphatidylinositol (GPI) attachment signals and a single epidermal growth factor-like (EGF-like) domain at their carboxyl termini. Nevertheless, the remainder of their protein coding regions are quite dissimilar. It appears that one of these genes arose as a result of a relatively ancient gene duplication event and both genes have subsequently diverged considerably. This study shows that msp5 is transcribed in asexual stages and its encoded product is a 40 kDa protein that appears to be located on the merozoite surface as determined by immunofluorescence assays.

A second merozoite surface protein (MSP-4) of Plasmodium falciparum that contains an epidermal growth factor-like domain

Merozoite surface proteins of Plasmodium falciparum play a critical role in the invasion of human erythrocytes by the malaria parasite. Here we describe the identification of a novel protein with a molecular mass of 40 kDa that is found on the merozoite surface of P. falciparum. We call this protein merozoite surface protein 4 (MSP-4). Evidence for the surface location of MSP-4 includes (i) a staining pattern that is consistent with merozoite surface location in indirect immunofluorescent studies of cultured parasites, (ii) localization of MSP-4 in the detergent phase in Triton X-114 partitioning studies, and (iii) nucleotide sequencing studies which predict the presence of an N-terminal signal sequence and a hydrophobic C-terminal sequence in the protein. Immunoprecipitation studies of biosynthetically labelled parasites with [3H] myristic acid indicated that MSP-4 is anchored on the merozoite surface by a glycosylphosphatidylinositol moiety. Of considerable interest is the presence of a single epidermal growth factor-like domain at the C terminus of the MSP-4 protein, making it the second protein with such a structure to be found on the merozoite surface.

Molecular variation in a novel polymorphic antigen associated with Plasmodium falciparum merozoites

A cDNA clone encoding part of a novel polymorphic merozoite antigen from Plasmodium falciparum was isolated by screening a cDNA library with human immune serum from Papua New Guinea. Immunofluorescence microscopy and immunoblotting with affinity-purified antibodies recognized a highly polymorphic antigen, Ag956, present in schizonts and merozoites. Biosynthetic labeling and immunoprecipitation experiments demonstrated that Ag956 is proteolytically cleaved during merozoite maturation. The complete genomic sequence of Ag956 from the D10 clone of P. falciparum isolate FC27 encodes a secreted protein of calculated molecular mass 43,243 that is very hydrophilic and contains a region of unusual heptad repeats of the general structure AXXAXXX. This antigen has been named the secreted polymorphic antigen associated with merozoites (SPAM). The sequence of a second SPAM allele from the 3D7 clone of isolate NF54 reveals that the alanine heptad repeats and the hydrophilic C-terminal half of the protein are conserved. Variation among SPAM alleles is the result of deletions and amino acid substitutions in non-repetitive sequences within and flanking the alanine heptad-repeat domain. Heptad repeats in which the a and d position contain hydrophobic residues generate amphipathic alpha-helices which give rise to helical bundles or coiled-coil structures in proteins. Thus, SPAM is the first example of a P. falciparum antigen in which a repetitive sequence has features characteristic of a well-defined structural element.

Allelic variants of the Plasmodium falciparum merozoite surface antigen 2 (MSA-2) in a geographically restricted area of Irian Jaya

Blood samples were collected from 12 residents of 4 villages in the Oksibil area of Irian Jaya. Eleven patients were positive for Plasmodium falciparum infection as evidenced by successful amplification of the MSA-2 gene by the polymerase chain reaction. Two patients showed evidence of infection by 2 strains of Plasmodium falciparum. All MSA-2 genes were completely sequenced and all could be assigned to one of the two major allelic families of MSA-2, however all MSA-2 gene sequences differed from previously described alleles. Five new allelic forms were identified, one of which was present in 8 of the 11 patients. Within small natural populations of P. falciparum, it appears that variation in MSA-2 approximates that seen world-wide. All samples were also analysed by hybridisation of amplified DNA to family specific probes and all samples hybridised to known probes. Our results demonstrate that there is a degree of microheterogeneity of MSA-2 that is undetectable by hybridisation studies alone.

Lactobacilli isolated from sugary kefir grains capable of polysaccharide production and minicell formation

Homo- and heterofermentative species of Lactobacillus have been isolated from sugary kefir grains. Most of the homofermentative strains fermented tagatose and aldonitol and presented 48-54% of homology with Lactobacillus paracasei ssp. paracasei NCDO 151 (ex Lactobacillus casei). The two variants of a hetero-fermentative species, although fermenting arabinose, were related to Lactobacillus hilgardii NCDO 264 (type strain) with 88% of homology. One of them produced polysaccharide from sucrose at pH 4.8 and 30 degrees C; the best glucose conversion into polysaccharide was obtained from 3% of sucrose (81.8%), and the maximum production occurred about 35 hours after the end of the log phase of growth, in MRS sucrose broth. Polysaccharide formation did not occur above 40 degrees C, a temperature at which no growth was observed. The two variants were forming minicells by abnormal divisions.

Integral membrane protein located in the apical complex of Plasmodium falciparum

We describe the cloning of a novel antigen of Plasmodium falciparum which contains a hydrophobic domain typical of an integral membrane protein. This antigen is designated apical membrane antigen 1 because it appears to be located in the apical complex. Apical membrane antigen 1 appears to be transported to the merozoite surface near the time of schizont rupture.

Influence of the lactoperoxidase system on susceptibility of the udder to Streptococcus uberis infection

Lactoperoxidase (LP), thiocyanate (SCN-), pH and somatic cell counts (SCC) were measured in mammary secretions from 20 cows collected 14 d before drying-off, 7 and 21 d after drying-off, and 3-18 d postcalving. The inhibitory activity of the secretions on Streptococcus uberis was determined and the susceptibility of the udder to infection by this organism was tested by intramammary infusion of 250 colony forming units at the above stages. LP, SCN-, pH and SCC increased during involution and fell postcalving. The secretions collected before drying-off, 7 d after drying-off and postcalving inhibited growth of Str. uberis.; those collected 21 d after drying-off did not. Inhibitory activity in pre-drying-off secretions was destroyed by heating and restored by addition of LP, glucose and glucose oxidase, but addition of these substances to secretion 21 d after drying-off did not provide a full inhibitory system. The growth of Str. uberis in the secretions was correlated with intramammary susceptibility, since challenges with Str. uberis at 14 d before drying-off, at 7 and 21 d after drying-off and postcalving led to 43.8, 25.0, 81.3 and 37.5% of quarters becoming infected. It is suggested that the LP/SCN-/H2O2 system plays a role in protecting the lactating mammary gland from infection with Str. uberis but becomes ineffective as involution progresses.

Influence of mastitis on growth of starter organisms used for the manufacture of fermented milks

The effect of milk containing increased somatic cells on the starter organisms Streptococcus thermophilus, Lactobacillus bulgaricus and L. acidophilus was examined. Increased somatic cell count resulted in stimulation of Str. thermophilus owing to increased proteolysis, but inhibition of L. acidophilus as a consequence of increased phagocytic activity of the polymorphonuclear leucocytes

A note on the heterofermentative Lactobacillus isolated from kefir grains

Heterofermentative lactobacilli have been isolated from kefir grains obtained from four different sources. A number of these isolates ferment only L-arabinose and gluconate and are similar to the species 'Lactobacillus desidiosus'. The DNA of these isolates, however, have 85-109% homology with 'L. caucasicus' NCDO 190 which is now regarded as L. kefir. The relationship between these strains is discussed.

Stimulation of Streptococcus thermophilus growth in mastitic milk

Growth of Streptococcus thermophilus was faster in mastitic milk, aseptically collected following intramammary infusion of Escherichia coli endotoxin, than in normal aseptically collected milk. The contribution of polymorphonuclear leucocytes (PMN), of plasma and plasmin to this stimulation has been investigated. Addition of plasmin to low cell count milk stimulated growth of the streptococcus to the same degree as mastitic milk. However, addition of plasma or PMN from blood or from milk were less stimulatory. The part played by these components in providing casein breakdown products for the weakly proteolytic Str. thermophilus in mastitic milk is discussed.

Comparison of the antibacterial activity of the hypothiocyanite anion towards Streptococcus lactis and Escherichia coli

It has been suggested that the antibacterial activity of the lactoperoxidase/thiocyanate/hydrogen peroxide system is due to the hypothiocyanite anion. Relatively pure solutions of hypothiocyanite can be prepared using an immobilized enzyme. These preparations have been used to examine the effect of the anion on the growth and on the membranes of Escherichia coli and Streptococcus lactis. Escherichia coli is killed in the presence of the anion whereas the effect on Streptococcus lactis is only bacteriostatic. As similar effects have been noted with the lactoperoxidase/thiocyanate/hydrogen peroxide system the hypothesis that the action of the two systems is similar is supported.

The antibiotic activity of the lactoperoxidase-thiocyanate-hydrogen peroxide system in the calf abomasum

The lactoperoxidase system which had been previously shown to kill Gram-negative organisms (eg, coliforms, salmonellae, pseudomonads) in vitro, was found to be activated in vivo. The lactoperoxidase was provided by the milk and the thiocyanate either by the milk or by its secretion in the abomasum. The third factor was provided either by a H2O2 generating system (glucose oxidase and glucose) or by H2O2 producing lactobacilli. The latter occur naturally in large numbers in the abomasum of the calf.

Influence of the heat treatment of human milk on some of its protective constituents

Human milk was subjected to heat treatments of graded severity and examined for its content of immunoglobulins, lactoferrin, lysozyme, vitamin B12-and folate-binder proteins, and lactoperoxidase. Holder pasteurization (62.5degrees C 30 minutes) reduced the IgA titer by 20%, and destroyed the small content of IgM and most of the lactoferrin. Lysozyme was stable to this treatment, but with an increase in temperature there was progressive destruction, to near 100% at 100degrees C. The same was broadly true of the capacity of milk to bind folic acid and potect it against bacterial uptake; with vitamin B12 the binder was more labile at 75degrees C than at 100degrees C. The milk contained no detectable lactoperoxidase.

Nonspecific bactericidal activity of the lactoperoxidases-thiocyanate-hydrogen peroxide system of milk against Escherichia coli and some gram-negative pathogens

Two strains of Escherichia coli and one strain each of Salmonella typhimurium and Pseudomonas aeruginosa were killed by the bactericidal activity of the lactoperoxidase-thiocyanate-hydrogen peroxide system in milk and in a synthetic medium. H2O2 was supplied exogenously by glucose oxidase, and glucose was produced at a level which was itself noninhibitory. Two phases were distinguished: the first phase was dependent on the oxidation of SCN(-) by lactoperoxidase and H2O2, which was reversed by reducing agent, and the second phase was dependent on the presence of accumulated H2O2, which was reversed by catalase. The latter enzyme could also reverse the first phase, but only when present in excessive and unphysiological levels. The bactericidal activity was greatest at pH 5 and below, and it depended on the SCN(-)concentration and on the number of organisms. Since raw or heated milk neutralizes the acid barrier against infection in the stomach, the bactericidal system discussed may contribute to the prevention of enteric infections in neonates.